Effect of Extreme Temperatures on the Coefficient of Thermal
coefficient of thermal expansion (CTE) is assumed to be constant for temperatures between 32 and 140°F (0 to 60°C) However, recent field analysis of an adjacent box-girder bridge with HSC girders connected using UHPC shear keys has shown that the actual temperature range experience by the UHPC-HSC was 14 to 100 4°F (-10 to 38°C)
COEFFICIENT OF THERMAL EXPANSION FOR VARIOUS MATERIALS AT
The coefficient of thermal expansion is defined as the change in length or volume of a material for a unit change in temperature The overall coefficient is the linear thermal expansion (in ) per degree Fahrenheit or Celsius The CTE data is calculated by the change in length divided by the quantity of
Reversible Temperature Coefficients
• Reversible Temperature Coefficient of Coercivity – Is a measure for the average of the change in Hci as a function of temperature – Is often referred to as (Greek letter beta) – The IEC proposes naming it “ (HcJ)” • Expressed as change per ºC (or K or ºF) • These are average values over a specified temperature range
Temperature Coefficient of Resistance for Current Sensing
The temperature coefficient of resistance (TCR), sometimes referred to as resistance temperature coefficient (RTC), is a characteristic of the thermal energy component of the above imperfections The effect of this resistance change is reversible as the temperature returns to reference temperature, assuming the grain structure was not altered
Temperature coefficient of resistivity
Temperature coefficient of resistivity Example: A platinum resistance thermometer has a resistance R 0 = 50 0 Ω at T 0=20 ºC α for Pt is 3 92×10-3 (ºC)-1 The thermometer is immersed in a vessel
Iterative calculation of the heat transfer coefficient
The heat transfer coefficient, h, is the most difficult parameter to be settled In this report it is shown a fast and easy iterative method to calculate the h value and later, the temperature of cooling for heat sink Introduction The heat transfer coefficient or convective coefficient (h), is used in thermodynamics to calculate the heat
Thermal expansion of technical solids at low temperatures; a
Table2 1 Linearthermalcontractionandcoefficientsoflinearthermalexpansion Elements Aluminuin Antimonyt Berylliumt Bismuth Cadmiumb T 10« dLjg ,£293-iT 106 dijg,£293
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VISHAY DALE
ResistorsWhite Paper
Temperature Coefficient of Resistance for Current Sensing www.vishay.comWHITE PAPER
Revision: 11-May-20201Document Number: 30405
For technical questions, contact: ww2bresistors@vishay.comTHIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT
ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000By Bryan Yarborough
HOW TEMPERATURE AND CONSTRUCTION AFFECT RESISTANCE STABILITYOBJECTIVE
1. What is TCR?
2. How is TCR determined?
3. How does construction affect TCR performance?
4. TCR in applications
5. How to compare datasheets
CAUSE AND EFFECT
(1) Resistance is a result of a combination of factors that cause an electron"s movement to deviate from an ideal path within a crystalline lattice of a metal or metal alloy. As an electron encounters defects or imperfections within the lattice it can cause diffusion. This increases the path traveled, resulting in an increased resistance. These defects and imperfections can result from: Movement in the lattice due to thermal energy Different atoms present in the lattice, such as impurities Partial or complete absence of a lattice (amorphous structure) Disordered zones at the grain boundaries
Crystalline and interstitial defects in the latticeNote (1) Source: Zandman, Simon, & Szwarc Resistor theory and technology 2002 p. 23 - p.24 The temperature coefficient of resistance (TCR), sometimes referred to as resistance temperature coefficient (RTC), is a characteristic of the thermal energy component of the above imperfections. The effect of this resistance change is reversible as the temperature returns to reference temperature, assuming the grain structure was not altered from high temperatures resulting from an extreme pulse / overload event. For Power Metal Strip® and Power Metal Plate products, this would be a temperature that caused the resistance alloy to exceed 350 °C. This resistance change due to temperature is measured in ppm/°C, which widely varies among different materials. For example, manganese-copper alloy has a TCR of < 20 ppm/°C (for 20 °C to 60 °C), whereas copper used interminations is approximately 3900 ppm/°C. Another way to represent ppm/°C that may be easier to consider is that
3900 ppm/°C is the same as 0.39 %/°C. These may seem
like small numbers until you consider the change in resistance due to a temperature rise of 100 °C. For copper that would cause a 39 % change in resistance. An alternate method for visualizing the effect of TCR is to consider it in terms of the rate of expansion of a material with temperature. Consider two different bars, A and B, that are each 100 m in length. Bar A changes length at a rate of +500 ppm/°C and bar B changes length at a rate of+20 ppm/°C. A temperature change of 145 °C will cause the length of bar A to increase 7.25 m, whereas bar B will only increase in length by 0.29 m. Below is a scaled (1 / 20) representation to visually demonstrate the difference. Bar A has a very noticeable change in length, whereas bar B has no visible change in length. This also applies to a resistor in that the lower TCR will result in a more stable measurement across temperature, which may be caused by applied power (causing the resistance element temperature to increase) or ambient environment.HOW TCR IS MEASURED
TCR performance per MIL-STD-202 Method 304 is
resistance change based on a reference temperature of25 °C. The temperature is changed and the device under
test is allowed to reach equilibrium before the resistance value is measured. The difference is used to determine the TCR. For the Power Metal Strip WSL model, the TCR is measured at the low temperature of -65 °C and then measured at +170 °C. The equation follows below. Typically an increase in resistance with an increase in temperature results in a positive TCR. Also, note that self-heating causes a resistance change due to TCR.T = 25 °C
T = 170 °CBar ABar A
Bar B Bar B Temperature Coefficient of Resistance for Current SensingWhite Paper
www.vishay.comVishay Dale
WHITE PAPER
Revision: 11-May-20202Document Number: 30405
For technical questions, contact: ww2bresistors@vishay.comTHIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENTARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000